A wide range of farming systems have been available for an extended period but only within the past 200 years has there been quantitative data to compare them for reliability and output. Improvements to husbandry and selection of plants and animals have enabled much greater production but have sometimes forced producers into a developmental pathway they may not have wished, as in the Green Revolution. Reconstituting traditional systems may avoid these problems. There may also be constraints on systems due to philosophical considerations, as in organic agriculture, environmental preferences or limits such as global warming or nitrate leaching, or wildlife conservation measures. New technologies such as precision farming and genetic modification may offer productivity and reliability advantages but their overall effect on systems may be very complex and not well understood. Intensification of systems may also create unforeseen problems such as soil erosion and salinity.